core js modules insertion breaks AMD exports

I’m submitting a bug report

Webpack Version: 4.16.0

Babel Core Version: 7.0.0-rc.1

Babel Loader Version: 8.0.0-beta.4

Please tell us about your environment: macOS 10.13.6, node v8.9.4, npm 6.3.0

Current behavior: When babel found a method that probably need a polyfill it is inserting

/***/ (function(module, __webpack_exports__, __webpack_require__) {

"use strict";
__webpack_require__.r(__webpack_exports__);
/* harmony import */ var core_js_modules_es6_regexp_replace__WEBPACK_IMPORTED_MODULE_0__ = __webpack_require__(/*! core-js/modules/es6.regexp.replace */ "../node_modules/core-js/modules/es6.regexp.replace.js");
/* harmony import */ var core_js_modules_es6_regexp_replace__WEBPACK_IMPORTED_MODULE_0___default = /*#__PURE__*/__webpack_require__.n(core_js_modules_es6_regexp_replace__WEBPACK_IMPORTED_MODULE_0__);

define(function (require, exports) {
  function getUppercase(featureName) {
    return featureName.replace(/-/g, '_');
  }

  exports.foo = function () {
    getUppercase();
  };

  exports.QUX = 'QUX';
});

/***/ }),

That is probably correct. But AMD code that follows it stops exporting it members.

Removing modules: false from .babelrc seems fix this issue, but is not desired, because of tree-shaking.

Console shows warnings:

WARNING in ./js/index.js 2:4-7
"export 'QUX' (imported as 'BAZ') was not found in './test'
 @ multi ./js/index.js

WARNING in ./js/index.js 2:0-3
"export 'foo' (imported as 'bar') was not found in './test'
 @ multi ./js/index.js

Expected/desired behavior: Without polyfills inserting, module exported correctly

/***/ (function(module, exports, __webpack_require__) {

var __WEBPACK_AMD_DEFINE_RESULT__;!(__WEBPACK_AMD_DEFINE_RESULT__ = (function (require, exports) {
  function getUppercase(featureName) {// return featureName.replace(/-/g, '_');
  }

  exports.foo = function () {
    getUppercase();
  };

  exports.QUX = 'QUX';
}).call(exports, __webpack_require__, exports, module),
				__WEBPACK_AMD_DEFINE_RESULT__ !== undefined && (module.exports = __WEBPACK_AMD_DEFINE_RESULT__));

/***/ }),

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem along with a gist/jsbin of your webpack configuration.

{
    "presets": [
        ["@babel/preset-env", {
            "modules": false,
            "useBuiltIns": "usage"
        }],
        "@babel/preset-react"
    ]
}

define(function(require, exports) {
    function getUppercase(featureName) {
        return featureName.replace(/-/g, '_');
    }


    exports.foo = function() {
        getUppercase();
    };

    exports.QUX = 'QUX';
});

• What is the expected behavior? Module exports it members regardless of polyfills inserting

• What is the motivation / use case for changing the behavior? Using webpack with multiple legacy modules

[loganfsmyth]

Oh right, for that you need to set sourceType: "unambiguous" so that Babel doesn’t just assume the file is an ES module.

[ogonkov]

Looks like sourceType fix AMD build